Conventionally, a floor of a vehicle body of a vehicle such as an automobile includes a main floor and a rear floor which are provided in front and rear sides of the vehicle, and a side sill extending in the vehicle front-and-rear direction is provided in each of left and right sides of the floor in a vehicle-width direction. In addition, a floor tunnel projecting in the upper direction of the vehicle and having a hat-like cross section is provided at a middle portion of the main floor in the vehicle width direction and extends in the vehicle front-and-rear direction. A vertical wall extending in a vehicle vertical direction is formed at a front side of the rear floor (see, for example, Patent Document 1).
In such a vehicle floor structure, steps are provided to the vertical wall of the rear floor in order to form a mount board for a rear seat and a projecting part for housing a fuel tank located in a lower position in the vehicle and to improve productivity. Further, for layout reasons, the height of the vertical wall of the rear floor is lower at the floor tunnel. Additionally, for reasons of layout for exhaust pipe arrangement, a rear end portion of the floor tunnel has a trumpet shape.
In some of conventional vehicles, the height of the rear portion of the floor tunnel is reduced gradually toward the rear of the vehicle in order to expand a foot space for the passenger sitting in the rear seat (see, for example, Patent Document 2).